WO2013061206A2 and JP2010205733A both discloses power line communication in lighting field. Their generally structures are having a modulator at the input AC mains side to modulate data onto the AC mains wave, and having a detector in the lighting fixture to extract the data from the AC mains wave and to using the data to control a power supply of the light source to deliver a power corresponding to the data.
WO2015070990A2 discloses a LED driving circuit with a current source to provide a constant current and a capacitor arrangement to be charged and discharge according to the instant amplitude of the input voltage. JP2011164258A discloses a LED flash device with a capacitor arrangement to be switched in parallel and charged by the battery, and to be switched in series and discharge the LED at a light emission timing.
A luminaire with a light source primarily serves to provide illumination. However, it may be possible for a light source to also fulfil a secondary function. An example of such a secondary function is visible light communication or coded light (CL), in which the radiant flux of the light source is modulated between a high radiant flux level (corresponding to “logic high”) and a low radiant flux level (corresponding to “logic low”). Data to be transmitted is provided as a bitstream of ones and zeros, and the lamp is driven to modulate its radiant flux accordingly. A CL receiver device with a suitable sensor (such as a photosensor) detects the different levels of radiant flux in the incident light, and converts the coded light information into a digital bitstream for further processing.
In principle, coded light is used to transfer a message from a conformant lamp to a receiver using visible light as the message carrier. The transferred message can indicate the lamp's location, and the lamp location information is further linked to location-related information such as positioning, navigation, advertisement and other applications. An LED light source is particularly well-suited to such an application on account of its essentially instantaneous response characteristics.
WO2012098486A1 discloses a circuit for CL communication, and discloses a Manchester code to encode data such that the logic high and logic low in the communication are balanced.
Changing the light intensity or radiant flux between high and low levels for signal transmission is a type of modulation. CL can be performed using amplitude modulation or pulse-width modulation (PWM). In amplitude modulation with an LED light source, the current amplitude flowing through the LED string is modulated, i.e. increased or decreased as appropriate, to achieve a corresponding increase or decrease in light intensity. A known CL modulator for an LED light source uses a post-regulator to increase or decrease the LED current as required, with a resistor to absorb or dissipate excess energy, so that this approach is associated with unfavourably high power consumption.
Therefore, it is an object of the invention to provide an improved coded light modulator.